Hydrology and Earth System Sciences Discussions www.hydrol-earth-syst-sci-discuss.net 1812-2108 1812-2116 6 2 2009 10.5194/hessd-6-3483-2009 http://www.hydrol-earth-syst-sci-discuss.net/6/3483/2009/ http://www.hydrol-earth-syst-sci-discuss.net/6/3483/2009/hessd-6-3483-2009.html http://www.hydrol-earth-syst-sci-discuss.net/6/3483/2009/hessd-6-3483-2009.pdf 3483 3515 2009-04-27 Comparison of different base flow separation methods in a lowland catchment A. L. Gonzales arpadgon@hotmail.com J. Nonner J. Heijkers S. Uhlenbrook UNESCO-IHE, Department of water engineering, P.O. Box 3015, 2601 DA, Delft, The Netherlands Hoogheemraadschap de Stichtse Rijnlanden – HDSR, P.O. Box 550, 3990 GJ, Houten, The Netherlands Delft University of Technology, Water Resources Section, P.O. Box 5048, 2600 GA, Delft, The Netherlands Assessment of water resources kept in different storages and moving along different pathways in a catchment is important for its optimal use and protection, and also for the prediction of floods and low flows. Moreover, understanding of the runoff generation processes is essential for assessing the impacts of climate and land use changes on the hydrological response of a catchment. Many methods for base flow separation exist, but hardly one focuses on the specific behaviour of temperate lowland areas. This paper presents the results of a base flow separation study carried out in a lowland area in the Netherlands. In this research, field observations of precipitation, groundwater and surface water levels and discharges, together with tracer analysis are used to understand the runoff generation processes in the catchment. Several tracer and non-tracer based base flow separation methods were applied to the discharge time series, and their results are compared. <br><br> The results show that groundwater levels react fast to precipitation events in this lowland area with shallow groundwater tables. Moreover, a good correlation was found between groundwater levels and discharges meaning that most of the measured discharge also during floods comes from the groundwater storage. It was determined using tracer hydrological approaches that approximately 90% of the total discharge is groundwater displaced by event water infiltrating in the northern part of the catchment, and only the remaining 10% is surface runoff. The impact of remote recharge causing displacement of near channel groundwater during floods could also be motivated with hydraulic approximations. 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